A conventional device for detecting contact between a hand and a steering wheel is proposed in PTL 1, for example. FIG. 17 shows a block circuit diagram of the detection device.
In FIG. 17, first oscillator 103 that includes first capacitor (capacity) 101 generates a first signal having frequency f1. First capacitor 101 is provided in a steering wheel (not shown) of a vehicle (not shown). First capacitor 101 may be a part of a heater existing in the steering wheel, for example.
Second oscillator 109 that includes second capacitor (capacity) 105 and third adjustable capacitor (capacity) 107 generates a second signal having second frequency f2. While no hand of a driver is put over the steering wheel, first and second frequencies f1 and f2 are equal to each other. Mixer 111 returns an absolute value of a difference between first and second frequencies f1 and f2. Frequency-voltage converter 113 converts the absolute value of the difference into output voltage U.
If a hand of the driver comes close to the steering wheel and ultimately takes hold of the steering wheel, first capacitor 101 comes under the influence of this action, and as a result, first frequency f1 changes. Voltage U continuously rises with a decrease in distance from the hand to the steering wheel. As soon as voltage U exceeds first threshold S1, the detection device detects contact between the hand and the steering wheel.